Gyromagnetic resonance methods and apparatus



Sept. 28, 1965 w, BELL 3,209,242

GYROMAGNETIC RESONANCE METHODS AND APPARATUS Original Filed Aug. 9, 1956W F 19. I 7

a INDICATOR N /2 DE- AND MODULATOR R e @/5 4 9 SWEEP FREQUENCY GEN.LIMITER DISCRIMINATOR @IS #43 ll VARIABLE gf g 2/ REACTOR FILTERINDICATOR AND (OSCILLATOR) VARIABLE REACTOR FIXED '33 34 OSC.

27 SWEEP @,25 OSC. 3!

IN VEN TOR.

GEN.

IZ8 26-@ F i 3 William E. Bell 34 6. pix-1 Attorney INDICATOR 69RECORDER i AM I vvvvv United States Patent 3,209,242 GYROMAGNETlCRESONANCE METHODS AND APPARATUS William E. Bell, Palo Alto, Calif,assignor to Varian Associates, San Carlos, Calif., a corporation ofCalifornia Continuation of application Ser. No. 604,295, Aug. 9, 1956.This application Mar. 13, 1963, Ser. No. 265,989 27 Claims. (Cl. 324-)The present application is a continuation application of US. Serial No.604,295 filed August 9, 1 956, and assigned to a common assignee. Theparent application has been abandoned in favor of the presentapplication.

The present invention relates in general to gyromagnetic resonancemethods and apparatus and more specifically to novel improved methodsand apparatus for detecting and displaying gyromagnetic resonance. Thepresent invention is extremely useful in that it provides a method andmeans whereby a single device may be utilized for inducing and detectinggyromagnetic resonance of a sample of matter and at the same timeachieving extremely high resolution of the gyromagnetic resonancesignals.

Heretofore, gyromagnetic resonance detection systems have been builtutilizing oscillating detector principles, that is, a system wherein theenergy absorbed from an oscillator is reflected as a change in theamplitude of oscillation or a change in the phase of the oscillation,such changes then being indicated and recorded to indicate resonance ofthe gyromagnetic sample. However, these prior art devices have failed toachieve high resolution due to uncontrollable random fluctuations anddrift in the frequency and the amplitude of the oscillations.

The present invention provides method and apparatus for stabilizing theoscillator such that the random fluctuations and drift of amplitude andfrequency are minimized, thereby allowing and providing extremely highresolution of the gyromagnetic resonance signals;

The principal object of the present invention is to provide novelimproved gyromagnetic resonance methods and apparatus whereby therelatively simple oscillating detector system may be utilized to observegyromagnetic resonance with extreme stability.

One feature of the present invention is the provision of an extremelystable frequency source, associated with the oscillating detectordevice, for controlling and stabilizing the frequency thereof.

Another feature of the present invention is the provision of anextremely stable frequency means providing a frequency standard forcomparison with the frequency.

of oscillation of the oscillating detector device whereby a controlsignal is derived to correct the frequency of the oscillating detector.

Another feature of the present invention is the provision of novelmethods and apparatus for detecting gyro-. magnetic resonance wherebyboth the absorption and dispersion characteristics of resonance may besimultaneously observed.

Another feature of the present invention is the provision of a variablereactor means coupled to the oscillator means and controlled by a signalfrom the stable frequency means for stabilizing the frequency of theoscillator detector means.

Another feature of the present invention is the provision of a noveloscillating detector which will give linear detection of gyromagneticresonance and which is relatively immune to lower frequency noisesignals.

These and other features and advantages of the present invention will bemore apparent after a perusal of the following specification taken inconnection with the accompanying drawings wherein,

ice

FIG. 1 is a schematic block diagram of a novel gyromagnetic resonancedetection system embodying the present invention,

FIG. 2 is a circuit diagram of a portion of the system of FIG. 1, and

FIG. 3 is a schematic block diagram of another gyromagnetic resonancedetection system embodying the present invention.

A description of the novel system embodying the present invention, asillustrated in the block diagram of FIG. 1, will firstbe made followedby a more detailed description of that portion of the system as is shownin the succeeding circuit diagram.

Referring now to FIG. 1 there is shown in block diagram form oneembodiment of the present invention. A sample of matter 1 which is underanalysis is placed within a strong D.C. polarizing magnetic fieldproduced, for example, by magnet 2. An R.F. coil 3 is positionedsurrounding thesample of matter 1 with its longitudinal axisperpendicular to the DC. magnetic flux lines of the polarizing field andforms the inductive portion of a tank circuit for an oscillator 4.

A sweep coil 5 is positioned. straddling. the sample of matter 1 and inoperation serves to superimpose upon the DC. magnetic field a smallcyclically varying magnetic field for modulating the polarizing magneticfield produced by magnet 2. A sweep generator 6 provides the lowfrequency current to drive the sweep coils 5.

In operation the oscillator 4 is tuned. to a fixed frequency, forexample 30 megacycles, and put into operation. The polarizing magneticfield produced by magnet 2 which may be, for example, an electromagnetis adjusted in intensity until its value is in the vicinity of thatvalue which is necessary to produce resonance of the sample of matter atan applied radio frequency of 30 megacycles. The sweep generator 6 thencyclically varies the magnetic field intensity to produce successiveresonance of the gyromagnetic bodies, if any, within the sample ofmatter 1.

When the gyromagnetic bodies within the sample of matter 1 pass throughresonance they will present to the.

oscillator 4, in succession, before resonance, a reactive impedance; atresonance, a purely resistive impedance; and then as resonance ispassed, a reactive impedance of the opposite sign than firstencountered. The effect of this changing impedance, due to the resonanceof the sample, on oscillator 4 is to, when the impedance is reactive,pull the frequency of the oscillator 4 either up or down in frequencydepending upon whether the imped ance of the gyromagnetic sample appearscapacitive or inductive. Precisely at resonance the impedance ispredominately resistive thereby lowering the Q of the tank or frequencydeterminative circuit of oscillator 4 and accordingly the amplitude ofoscillation. Thus, it can be seen as the sweep generator sweeps themagnetic field through resonance the amplitude of oscillator 4 will bemodulated.

This amplitude modulation is removed from the RF. signal by demodulator7 and fed to an indicator and recorder 8 to be recorded as a function ofsweep generator sweep or time as desired. The low frequency signalindicated and recorded in indicator and recorder 8 arising from theresistive characteristic of the sample of matter at resonance, isreferred to as the absorption signal.

For high resolution spectroscopy it is necessary that the oscillator 4remain substantially fixed at a given frequency. This is immediatelyapparent when one considers the numbers involved. For example, thebandwidth of the resonance of a particular gyromagnetic sample disposedwithin the polarizing field of approximately 7,000 gauss at a resonancefrequency of approximately 30 megacycles may well be between 1 and 3cycles.

3 Thus, it is very important that the oscillator frequency not vary acycle or a fraction of a cycle per second during the time required tosweep through the gyromagnetic spectrum of the sample 1.

Considering the reactive effects of the sample tending to detune theoscillator 4 it can be readily appreciated that for high resolution worksome means must be provided for holding the frequency of the oscillator4 constant. Accordingly, a portion of the R.F. output of oscillator 4 isfed to a limiter 9 wherein the signal is limited in alniplitude and thenapplied to a frequency discriminator The frequency discriminator 11 mustbe able to discriminate a cycle or a fraction of a cycle at 30megacycles. A carefully designed crystal controlled frequencydiscriminator is capable of obtaining the necessary discrimination. Sucha discriminator is taught by John Ruston in an article titled A SimpleCrystal Discriminator for FM. Oscillator Stabilization, appearing in theProc. IRE, of July 1951, pages 783-788. The output of the frequencydiscriminator 11 will be of a very low frequency or D.C. signal, themagnitude and phase of which is proportional to the degree and senserespectively that the frequency of oscillator 4 varies from thepreselected fixed reference value designed into the frequencydiscriminator 11.

The output of frequency discriminator 11 is then fed to a low passfilter 12 wherein extraneously induced higher frequency signals areeliminated. The low frequency signal is then fed to a variable reactor13 which is coupled into the oscillator 4 in such a manner as to varythe frequency of the oscillator 4 to keep it precisely at the frequencyas determined by the frequency discriminator 11.

As the magnetic polarizing field is swept through resonance agyromagnetic sample of matter 1 will first present a certain reactiveimpedance to oscillator 4 and then on the opposite side of resonance thesample will present the complementary reactive impedance. Theseimpedance changes due to the resonance of the sample tend to detune theoscillator 4. Thus, the frequency discriminator 11 will produce D.C. orlow frequency signals which are fed to the variable reactor to balanceout the reactive effects due to the sample 1.

On. one side of resonance the D.C. control signal will have a certainmagnitude and phase and on the opposite side of resonance it will haveequal magnitude but opposite phase. This amplitude change and phaseshift of the D.C. control signal as the sample passes through resonanceis indicative of the reactive characteristic of the sample and is knownin the art as the dispersive characteristic. The low frequency output offrequency discriminator 11 varies in accordance with the dispersivecharacteristic of the sample and thus is known as the dispersive signal.The dispersive signal is applied to an indicator and recorder 14 toallow observation of the dispersive characteristic of the sample 1.

Although in a preferred embodiment of the present invention, shown inFIG. 1, a separate limiter 9 has been shown and described, a separatelimiter is not required if one is willing to sacrifice some of thesensitivity of the absorption signal. More specifically, the oscillator4 may be operated at a saturated state thereby achieving the limitingfunction without a separate limiter means. In addition, low pass filter12 may be eliminated at the expense of a small amount of noise in thedispersion signal.

Referring now to FIG. 2 there is shown a circuit diagram of theoscillator 4 including the tuned tank or frequency determinativecircuit. The sample of matter 1 is disposed within the R.F. coil 3 whichtogether with a variable capacitor 15 and a variable inductor 16 formsthe tank or frequency determinative circuit of oscillator 4. The tankcircuit is tuned to the standard frequency as determined by the crystalof the frequency discriminator 11. In operation slight adjustments inthe tuning of 4 the tank circuit are accomplished by changing theeffective inductance of the tank circuit through the intermediary of thevariable reactor 13.

The oscillator 4 comprises a double triode having the output of the tankcircuit connected to the grid of the first triode 17a which is connectedas a cathode follower. The R.F. output of the cathode follower 17a iscoupled by a coupling capacitor 18 to the cathode of the second triodeamplifier 17b. The output of the second triode is taken from the platecircuit thereof via lead 19 through attenuating resistor 25 and couplingcapacitor 22 back to the tank circuit. A suitable tube for theoscillator 4 is, for example a 5814A. A second coupling capacitor 23 inthe plate circuit of the oscillator couples the amplified R.F. signal tothe demodulator 7. Representative values of the various elements used ina typical oscillator circuit, operating at 3 me., are as shown in thedrawings (FIG. 2).

The coupling capacitor 18 which serves to couple the output of thecathode follower 17a to the input of the second triode 17b is designedto pass only the higher frequency signals or the tuned circuit resonancefrequency. In this manner extraneously induced lower frequencyperturbations detected by the tuned circuit or otherwise appearing inthe output of cathode follower 17a are strongly attenuated by capacitor18 and thus are substantially not propagated to the input of triodeamplifier 17b.

Referring now to FIG. 3 there is shown another embodiment of the presentinvention. A sample of matter 25 which it is desired to analyze isplaced within a strong D.C. polarizing magnetic field produced by magnet26. An R.F. coil 27 is positioned surrounding the sample of matter withits longitudinal axis at right angles to the flux lines of thepolarizing field. A pair of sweep coils 28 are positioned straddling thesample of matter 25. The axis of the sweep coils 28 are in alignmentwith the D.C. polarizing field such as to facilitate modulation thereof.A sweep generator 29 applies a low frequency cyclically varyingenergizing current to sweep coils 28.

The R.F. coil 27 forms the inductive portion of a tuned tank circuit ofan oscillator 31. Oscillator 31 may be of the type that is shown anddescribed in FIGS. 1 and 2 above. The tank circuit of oscillator 31 iscoupled by a transmission line 32 to the output of a fixed frequencyoscillator 33 such as, for example, a stable crystal-controlledoscillator. A diode detector 34 is coupled as by, for example, inductivecoupling to the transmission line 32 interconnecting the oscillators 31and 33. The output of diode detector 34 is fed to an indicator andrecorder 35 for indicating the circulating currents present ontransmission line 32.

In operation, the fixed oscillator 33 is tuned to a fixed frequency suchas, for example, 30 megacycles. Oscillator 31 is tuned to the samefrequency as the fixed oscillator 33. The intensity of the D.C.polarizing magnetic field produced by magnet 26 is selected to be withinthe vicinity of resonance of the gyromagnetic sample 25 at the fixedfrequency of oscillator 31. A modulation of the D.C. polarizing fieldintensity is achieved by superimposing a small cyclically varyingbiasing field produced by sweep coils 28 and sweep generator 29 upon theD.C. polarizing field.

Modulation of the D.C. polarizing magnetic field intensity producessuccessive resonance of the gyromagnetic bodies within the sample ofmatter 25. Due to the coupling between oscillators 31 and 33 viatransmission line 32, oscillator 31 will tend to oscillate in phase andat the same frequency as fixed frequency oscillator 33. When oscillators31 and 33 are in phase their amplitudes are selected to be slightlyunequal and therefore there will be produced a voltage drop at the R.F.frequency across the inductive coupler present in transmission line 32.A corresponding constant amplitude R.F. signal will be produced in thesecondary of the inductive coupler which is the input to the diodedetector 34. The R.F. signal will be rectified in diode detector 34 andwill produce a steady DC signal in the input to indicator and recorder35.

As gyromagnetic resonance is approached in sample there will be producedan additional reactive impedance component, due to the sample, in thetank circuit of oscillator 31. This reactive component will tend todetune oscillator 31. However, due to the close coupling betweenoscillator 31 and fixed oscillator 33 via transmission line 32 beforeoscillator 31 can vary in frequency it must pull the frequency fixedoscillator 33 with it. However, fixed oscillator 33 will not be detuned,that is, it cannot be pulled off frequency by oscillator 31. Thus,balancing reactive currents will flow between oscillator 31 and 33 intransmission line 32 to balance out the reactive effects of the sample25 near resonance. These reactive currents are at the R.F. frequency offixed oscillator and are superimposed upon the existing R.F. voltagedrop across the inductor of transmission line 32.

The circulating R.F. currents will then be detected in diode detector 34and manifested as an increase or decrease in the DC. level in the outputof diode detector 34 which is then indicated and recorded on indicatorand recorder 35. Since the circulating currents which flow intransmission line 32 near resonance of the gyromagnetic sample 25 are afunction of the reactive effects of the sample 25 they are a measure ofthe dispersive characteristics of the sample and accordingly will havethe characteristic dispersive line shape.

Oscillator 31 may take the same form as the oscillator 4 of FIG. 1 shownin greater detail in FIG. 2. Fixed frequency oscillator 33 may be anyextremely stable oscillator such as, for example, a stablecrystal-controlled oscillator. Although the diode detector 34 is showninductively coupled to the transmission line 32 other forms of couplingsuch as, for example, capacitive coupling could also be used. Inaddition other demodulators could be used instead of a diode detector34.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of producing stable gyromagnetic resonance of a sample ofmatter disposed within a polarizing field region comprising the steps ofproducing gyromagnetic resonance of a sample of matter which iselectromagnetically closely coupled to the frequency determinativeresonant circuit of an R.F. oscillator means, such that resonanceeffects of the sample substantially tend to pull the frequency of saidoscillator means sampling a first R.F. resonance output frequency signalof the oscillator means, comparing a first R.F. resonance outputfrequency signal with a second R.F. fixed standard frequency, saidstandard frequency being independent of said R.F. oscillator and saidgyromagnetic resonance sample of matter deriving an electrical controlsignal from the comparison of the first and second R.F. frequencies forstabilizing the frequency of said oscillator means against said samplepulling effect and applying the control signal to the oscillator formaintaining the frequency thereof at the desired frequency andmonitoring the resonance whereby random fluctuations in the oscillationof the oscillator are minimized in use thereby enhancing stablegyromagnetic resonance.

2. The method according to claim 1 wherein the step of comparing thefirst R.F. resonance output frequency signal with the second R.F.standard frequency comprises the step of applying the output resonancefrequency signal to a stable fixed frequency discriminator.

3. The method according to claim 2 wherein the step of deriving acontrol signal for stabilizing the oscillator comprises the step ofderiving a low frequency signal, the

phase and magnitude of which is a function of the sense and degree towhich the frequency of the R.F. oscillator tends to vary from the R.F.standard frequency.

4. The method according to claim 1 wherein the step of applying thecontrol signal to the oscillator comprises the step of varying theinductance of the frequency determinative circuit of the oscillator invariable accordance with the control signal.

5. The method of observing stable gyromagnetic resonance of a sample ofmatter disposed within a polarizing field region by observing the affectof the resonating gyromagnetic bodies upon an oscillator comprising thesteps of producing gyromagnetic resonance of a sample of matter closelycoupled to the frequency determinative resonant circuit of theoscillator, such that resonance effects of said sample substantiallytend to pull the frequency of said oscillator comparing the output R.F.frequency of the oscillator with a standard R.F. fixed frequency,deriving an electrical control signal for stabilizing the oscillator,applying the control signal to the oscillator for maintaining thefrequency at the desired frequency, and measuring the control signal asa function of time to obtain a measure of the dispersive characteristicsof the gyromagnetic sample near resonance.

6. The method of observing stable gyromagnetic resonance of a sample ofmatter disposed within a polarizing field region by observing the affectof the resonating gyromagnetic bodies upon an oscillator meanscomprising the steps of producing gyromagnetic resonance of a sample ofmatter closely coupled to the frequency determinative resonant circuitof the oscillator means such that resonance effects of said samplesubstantially tend to pull the frequency of said oscillator, comparingthe output R.F. frequency signal of the oscillator means with a standardR.F. fixed frequency, said standard frequency being independent of theR.F. oscillator and the gyromagnetic resonance sample of matter,deriving in electrical control signal for stabilizing the oscillator,applying the control signal to the oscillator for maintaining the outputfrequency at the desired frequency signal, and measuring thefluctuations in the amplitude of oscillation of the oscillator means inthe vicinity of resonance to obtain a measure of the absorptioncharacteristics of the gyromagnetic sample of matter.

7. Apparatus for producing stable gyromagnetic resonance of a sample ofmatter disposed within a polarizing field region comprising, anoscillator means having its frequency determinative resonant circuitclosely coupled to the gyromagnetic resonance of the sample, such thatresonance effects of the sample substantially tend to pull the frequencyof said oscillator means, means forming an R.F. fixed frequency standardindependent of the R.F. oscillator and the gyromagnetic resonance sampleof matter, means for comparing the R.F. oscillations of the oscillatorto be the preselected R.F. standard frequency to obtain an electricalcontrol signal for controlling the oscillations of the oscillator, andmeans for applying the control signal to said oscillator means forcorrecting and stabilizing the R.F. oscillations thereof, and means formonitoring the resonance, thereby enhancing the stability ofgyromagnetic resonance by minimizing random fluctuations in theoscillations of the oscillator means.

8. Apparatus as claimed in claim 7 including a sweep means forcyclically varying the conditions necessary for gyromagnetic resonanceto thereby obtain successive gyromagnetic resonances of the gyromagneticbodies within the sample of matter.

9. Apparatus according to claim 7 wherein said monitoring means includea demodulator means coupled to said oscillator means for obtaining asignal in variable accordance with low frequency amplitude fluctuationsof said oscillator means, and indicator means: for indicating the lowfrequency amplitude fluctuations to thereby obtain an indication of theabsorption characteristics of the sample of matter.

10. An apparatus as claimed in claim 7 wherein said means for applyingthe control signals to said oscillator means comprises a transmissionline means.

11. Apparatus according to claim 8 including indicator means forindicating the control signals to thereby obtain a measure of thedispersive characteristics of the sample of matter.

12. Apparatus according to claim 10 wherein said monitoring meansincludes, demodulator means coupled to said transmission line means fordetecting the low frequency fluctuations in the control signals, andindicator means for displaying the magnitude and phase of the lowfrequency fluctuations of the control signals.

13. An apparatus as claimed in claim 11 wherein said RF. frequencystandard means comprises a frequency discriminator means, and said meansfor applying the control signals to said oscillator comprises a variablereactor means.

14. Oscillator apparatus for producing stable gyromagnetic resonance ofa sample of matter disposed within a polarizing magnetic field regioncomprising: a high Q resonator circuit resonant at the gyromagneticresonance frequency of said sample in said field, said sample beingelectromagnetically closely coupled to said high Q resonant circuit,cathode follower means including a cathode, a control grid and a plateelectrode, said cathode follower means having an input terminal thereofcoupled to said resonator circuit, amplifier means including its ownseparate cathode, control grid and plate electrode, circuit meanscoupling the output of said cathode follower means to the input of saidamplifier means, said circuit means including means for passingessentially only frequencies at said gyromagnetic resonance frequencyand for rejecting direct current and lower frequencies whereby lowfrequency perturbations are not coupled from said cathode followeroutput to said amplifier means, and feedback means for feeding back aportion of the output signal of said amplifier to said cathode followermeans in the proper phase to produce sustained oscillation of theoscillator apparatus at said gyromagnetic resonance frequency.

15. Apparatus as claimed in claim 14 including variable inductive meanscoupled to said resonator whereby the resonant frequency of saidresonator may be varied as desired.

16. An apparatus as claimed in claim 15 wherein said high pass couplingmeans comprises a coupling capacitor presenting a low impedance at theRF. resonant frequency of said resonator means and a substantiallyhigher impedance at a lower audio frequencies.

17. An apparatus as claimed in claim 14 wherein said coupling meanscouples together the separate cathode electrodes of said cathodefollower means and said amplifier means.

18. Gyromagnetic spectrometer apparatus comprising radio frequencyoscillator means for producing gyromagnetic resonance of a sample ofmatter disposed within a polarizing field and for detecting thecharacteristics of the sample of matter near resonance, limiter meanscoupled to said oscillator means for limiting the amplitude of theoscillations derived from said oscilator means, RF. frequencydiscriminator means for comparing the frequency of said RF. oscillatormeans with a standard fixed radio frequency to derive a low frequencycontrol signal the phase and magnitude of which is a function of thesense and degree to which the oscillating radio frequency of saidoscillator means varies from the standard radio frequency, low passfilter means for filtering out extraneously induced signals from the lowfrequency control signal, variable reactor means controlled by thecontrol signal to vary the frequency of said oscillator means intocoincidence with standard RF. frequency, demodulator means coupled tosaid R.F. oscillator means for detecting amplitude modulationsuperimposed upon the R.F. frequency of oscillation of said oscillatormeans the amplitude modulation being a measure of the absorption ofenergy by the sample from said oscillator means at sample resonance,indicator means for displaying the amplitude modulation signal, andsweep generator means for modulating the polarizing field over thesample of matter to produce successive gyromagnetic resonance of thegyromagnetic bodies, if any, within the sample of matter.

19. Apparatus according to claim 18 including second indicator means forindicating and displaying the control signals to thereby obtain ameasure of the dispersive characteristics of the sample of matter.

20. Gyromagnetic spectroscopy apparatus comprising first oscillatormeans having its frequency determinative resonant circuit closelycoupled to a sample of matter such that resonance effects of the samplesubstantially tend to pull the resonant frequency of said firstoscillator means, said sample being disposed within a polarizing fieldfor producing gyromagnetic resonance of the gyromagnetic bodies, if any,within the sample of matter, said oscillator means also serving fordetecting gyromagnetic resonances within the sample of matter, sweepgenerator means for producing a modulation of the DC. polarizing fieldover the sample of matter to thereby produce successive gyromagneticresonances of the gyromagnetic bodies within the sample of matter,second fixed frequency oscillator means for establishing a standardfrequency, transmission line means electromagnetically coupling saidfirst oscillator means and said second fixed oscillator means forallowing circulating reactive control currents substantially at thefrequency of the standard frequency to flow between said first and saidsecond oscillator means, diode detector means coupled to saidtransmission line means for detecting the circulating control currentsflowing within said transmission line means between said first and saidsecond oscillator means, and indicator means for indicating the outputof said diode detector means thereby obtaining a measure of thedispersive characteristics of the sample of matter near resonance.

21. Apparatus for producing stable gyromagnetic resonance of a sample ofmatter disposed within a polarizing field region comprising: oscillatormeans having a frequency determinative resonant circuit closely coupledto the gyromagnetic resonance of the sample; such that resonance effectsof the sample substantially tend to pull the frequency of saidoscillator means, means forming an RF. fixed frequency standardindependent of the RF. oscillator and gyromagnetic resonance sample ofmatter; means for comparing the RF. oscillations of the oscillator to bethe preselected R.F. standard frequency to obtain an electrical controlsignal for controlling the oscillations of the oscillator; means forapplying the control signal to said oscillator means for correcting andstabilizing the R.F. oscillations thereof, thereby enhancing thestability of gyromagnetic resonance by minimizing random fluctuations inthe oscillations of the oscillator means; and said oscillator meanscomprising, a high Q resonator means, forming the frequencydeterminative resonant circuit of said oscillator means, cathodefollower means having an input terminal thereof coupled to saidresonator means, amplifier means, said amplifier means and said cathodefollower means having separate D.C. emitter circuits, essentially onlyhigh pass coupling means serving to couple the output of said cathodefollower means to the input of said amplifier means whereby lowfrequency perturbations are not coupled to said amplifier means, andfeedback means for feeding back a portion of the output of saidamplifier means to the input of said cathode follower means in theproper phase to produce sustained oscillation of the oscillator means.

22. Apparatus as claimed in claim 21 including a sweep means forcyclically varying the conditions necessary for gyromagnetic resonanceto thereby obtain successive gyromagnetic resonances of the gyromagneticbodies within the sample of matter.

23. Apparatus according to claim 22 including indicator means forindication of the control signals to thereby obtain a measure of thedispersive characteristics of the sample of matter.

24. Apparatus as claimed in claim 23 wherein said RF. frequency standardmeans comprises a frequency discriminator means, and said means forapplying the control signals to said oscillator comprises a variablereactor means.

25. Apparatus according to claim 21 including a demodulator meanscoupled to said oscillator means for obtaining a signal in variableaccordance with low frequency amplitude fluctuations, if any, of saidoscillator means, and indicator means for indicating the low frequencyamplitude fluctuations to thereby obtain an indication of the absorptioncharacteristics of the sample of matter.

26. Apparatus as claimed in claim 21 wherein said means for applying thecontrol signals to said oscillator means comprises a transmission linemeans.

27. Apparatus according to claim 26 including demodulator means coupledto said transmission line means for detecting the low frequencyfluctuations in the control signals, and indicator means for displayingthe magnitude and phase of the low frequency fluctuations of the controlsignals.

References Cited by the Examiner UNITED STATES PATENTS 1/59 Batchelor331167 3/59 Sontheimer 331-36 OTHER REFERENCES Tinkham: Physical Review,Vol. 97, No. 4, Feb. 15, 1955, pages 951-966 incl. (QC-1P4).

Beringer et a1.: Physical Review, Vol. 95, No. 6, Sept. -15, 1954, pages1474-1481 incl. (QC-1P4).

Hirshon et a1.: The Review of Scientific Instruments, Vol. 26, No. 1,January 1955, pages 34-40 incl. (Q 187- R5).

Pound: The Review of Scientific Instruments, Vol. 17, No. 11, November1946, pages 490-505 (Q-184-R5).

Ingram: Spectroscopy at Radio and Microwave Frequencies, ButterworthsScientific Publications, London, 1955, pages 102-105 incl. (QC 454-15).

CHESTER L. JUSTUS, Primary Examiner.

MAYNARD R. WILBUR, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,209,242 September 28, 1965 William E. Bell It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 6, line 37, for "in" read an line 55, strike out "be"; column 7,line 71, after "with" insert the column 8, line 20, after "said" insertfirst same column 8, line 49, strike out "be".

Signed and sealed this 6th day of December 1966.

( Awest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. THE METHOD OF PRODUCING STABLE GYROMAGNETIC RESONANCE OF A SAMPLE OFMATTER DISPOSED WITHIN A POLARIZING FIELD REGION COMPRISING THE STEPS OFPRODUCING GYROMAGNETIC RESONANCE OF A SAMPLE OF MATTER WHICH ISELECTROMAGNETICALY CLOSELY COUPLED TO THE FREQUENCY DETERMINATIVERESONANT CIRCUIT OF AN R.F. OSCILLATOR MEANS, SUCH THAT RESONANCEEFFECTS OF THE SAMPLE SUBSTANTIALLY TEND TO PULL THE FREQUENCY OF SAIDOSCILLATOR MEANS SAMPLING A FIRST R.F. RESONANCE OUTPUT FREQUENY SIGNALOF THE OSCILLATOR MEANS, COMPRISING A FIRST R.F. RESONANCE OUTPUTFREQUENCY SIGNAL WITH A SECOND R.F. FIXED STANDARD FREQUENCY, SAIDSTANDARD FREQUENCY BEING INDEPENDENT OF SAID R.F. OSCILLATOR AND SAIDGYROMAGNETIC RESONANCE SAMPLE OF MATTER DERIVING AN ELECTRICAL CONTROLSIGNAL FROM THE COMPARISON OF THE FIRST AND SECOND R.F. FREQUENCIES FORSTABILIZING THE FREQUENCY OF SAID OSCILLATOR MEANS AGAINST SAID SAMPLEPULLING EF-